Kinetics of division of CD45^midlin⁻Rho⁻SP cells cultured in different SF concentrations. A total of 130 cells (n = 56 for 300 ng/mL, n = 58 for 10 ng/mL, and n = 16 for 1 ng/mL) were deposited individually into 96-well plates, visually confirmed to be single cells, and then observed every 4 to 6 hours to determine their kinetics of division. A cell was scored as having undergone a first division when a second cell could be observed in the well and a second division when a third cell could be seen. There was less than 1% cell death when the cells were cultured in either 10 or 300 ng/mL SF. A Lowess spline curve was generated in GraphPad Prism (version 4.03) using 248 values estimated based on the marked values in the time course and is shown for each of the first and second divisions under each condition.